The banking royal commission heard the incorrect witnessing of the beneficiary nomination forms for superannuation funds could have potentially rendered the final wishes of 2520 NAB customers invalid.

Senior NAB executive Andrew Hagger said the bank had acted to ensure the customers were not affected, noting most of the clients had re-signed their forms.

"We have dealt very comprehensively to the client issue, and that was our prime concern that through our own sloppiness we had created this situation which could affect the peace of mind of 2520 customers," Mr Hagger told the inquiry on Tuesday.

About 325 NAB staff, 204 of them financial advisers, were found to have failed to correctly witness forms setting out who individuals want to receive their superannuation funds when they die.

Mr Hagger said the staff thought they were taking a shortcut in the interests of the client but it was clear on the form that witnesses had to be present when it was signed.

"I think a social norm had crept in and become entrenched."

NAB sacked one adviser, Bradley Meyn, who forged a couple's initials on the forms, which Mr Hagger said crossed the line.

Other staff were given an amnesty to come forward, with those financial advisers losing 25 per cent of their bonuses.

The commission heard a number of regional wealth executives also suffered consequences as well as the leaders of NAB's wealth advice business.

In a November 2017 email, NAB CEO Andrew Thorburn noted those involved in the issue had somewhere between 20 and 100 per cent of their bonuses reduced for the year.

Mr Hagger, the chief customer officer in NAB's consumer banking and wealth management division, said customers expected action at the management and leadership level.

Mr Hagger had his 2017 bonus cut by about $60,000, but still received $960,000.

The inquiry heard NAB's executive manager of wealth advice Greg Miller was among those opposed to any implications for the wealth leadership team.

"He said that this was an important cultural symbol and that what the organisation was really encouraging then was for ben noms (beneficiary nomination) style issues to be swept under the carpet in future," Mr Hagger wrote in a file note.

"He said we risked key departures, and all at a time when there's a possibility we will look to sell the advisory business or parts of it in the coming year."

Mr Miller left NAB in December as part of a restructure of its wealth division.

He received no bonus for 2017, Mr Hagger said.

NAB Financial Planning general manager Tim Steele had his bonus shaved by 10 per cent.

Australian Associated Press